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Old 4th June 2008, 05:52 AM   #1021
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Any small signal TR having turn-on Vbe of about 0.66 will work.
Papa likes ZTX, but it does not limit your choice with others in this case...
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Old 4th June 2008, 01:55 PM   #1022
udailey is online now udailey  United States
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I have three 1240VA transformers that I picked up on ebay a while ago. Problem is... 29V output at no load and 27.2 at 19Amps. What do you guys think about using a voltage regulator to drop the voltage down to 24V (voltage would differ I guess depending on placement of the regulator)? If you think its not a problem would you put the regulator circuit between the transformer and the power supply or between the power supply and the amp?
Thanks
Uriah

figure I might add some info on these
Primary is 120V 50Hz
Secondaries are 27.2V at 19Amps
Secondaries are 29.6V at No Load
Primary resistance 2x(.34+.13)
Secondary resistance 4x.065 ohm
Temp rise at 1240VA is 80 deg C
P/N is TI-043222B AU Iss 0 from Toroid International Ltd.
DIA is 165mm and Height s 98mm weight is 10.2kg
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Old 4th June 2008, 02:30 PM   #1023
juma is offline juma  Germany
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The voltage regulator is an option, but a costly one - it will demand the heatsink of his own, almost as big as amplifier's.
If I were you, I'd rather unwound the secondaries to get a desired voltage on them.
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Old 4th June 2008, 02:32 PM   #1024
udailey is online now udailey  United States
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Unfortunately they are potted. Which is really nice for mounting them and not so nice for unwinding
Uriah
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Old 4th June 2008, 02:50 PM   #1025
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by udailey
I have three .......
seems that using cap multipliers ( with mosfets as pass elements) is logical ....
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Old 4th June 2008, 03:21 PM   #1026
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Quote:
Originally posted by udailey


What do you guys think about using a voltage regulator to drop the voltage down to 24V (voltage would differ I guess depending on placement of the regulator)? If you think its not a problem would you put the regulator circuit between the transformer and the power supply or between the power supply and the amp?

I would use ZV5 regulator, but with C-R-C filter instead of C-L-C.
The total heat dissipation/channel is the same whether you have
the regulator or not.
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Old 4th June 2008, 03:28 PM   #1027
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Quote:
Originally posted by udailey
29V output at no load and 27.2 at 19Amps.
Mmm, (cough), let's hope these are DC numbers.
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Old 4th June 2008, 05:18 PM   #1028
udailey is online now udailey  United States
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I read about voltage dividers on this site after reading Zen Mod's response:
http://www.aikenamps.com/VoltageDividerRule.htm
I came up with this:
Capacitive dividers can be used with AC input signals.

Vout = Vin*C1/(C1+C2)

Example: In the following circuit, the output voltage could be: Vout = 28VAC*1uF/(1uF + 0.22uF) = 22.95VAC. Note that the output voltage is not dependent on the input frequency. However, if the reactance of the capacitors is not large at the frequency of interest (i.e. capacitance not large enough), the output current capability will be very low.


Click the image to open in full size.
I tried to stick a pic in here. Dont know where it went, but here is the link.
http://picasaweb.google.com/udailey/...75545305807906


So can I just use this on the secondaries before the rest of the power supply circuit?
If I can, then does this little circuit go on the + and - of the secondary or just on one of them?
Thanks so much,
Uriah
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Old 4th June 2008, 05:32 PM   #1029
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by udailey
I read about voltage dividers on this site after reading Zen Mod's response:......

what I meant is really like this cap multiplier implemented in F3 (look attachment) .

that way you'll loose 4-5V with benefits .....
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File Type: jpg f3-service-manual-sm(2)-1.jpg (69.2 KB, 2205 views)
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Old 4th June 2008, 06:28 PM   #1030
udailey is online now udailey  United States
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Hmm. Really does not make any sense to me. I wont try to pretend that I get it But I will try to understand it so I dont waste anyones time.
I tried reading up on voltage multipliers but for my situation it really didnt make sense. Plus that F3 is the amp not the power supply where I have the problem, but then again I dont understand the circuits anyway and I kind of need to be led by the hand at this point.

If I have a schematic I can replicate it and maybe even have it work but I dont actually understand the circuit. I do understand algebraic equations in circuits. So if you were to say I need to use a voltage divider circuit with Vout=Vin*C1/(C1+C2) and put that circuit on each secondary lead in between the transformer and the rest of the PSU circuit, then I would understand how to do that. But right now thats the limit of "getting it" for me.

In short, I am still left baffled. It seems like you guys think its possible for me to use my 27-29Vout transformer and it would probably save me a lot of money to be able to do that. Is there a simple way to do so? If you would be so kind as to show me I certainly would appreciate it.
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